The present invention relates to power control for wireless communication systems and, in particular, fast adaptive power control system and methods for a variable multirate communication system.
Various methods of power control for wireless communication systems are well known in the art. An example of an open loop power control transmitter system for a single rate data system is illustrated in FIG. 1. An example of a closed loop power control transmitter system for a single rate data is illustrated in FIG. 2.
The purpose of both systems is to rapidly vary transmitter power in the presence of a fading propagation channel and time-varying interference to minimize transmitter power while insuring that data is received at the remote end with acceptable quality. Typically, in a digital implementation, transmitter power is varied by applying a varying scale factor to the digital data, as opposed, for example, to varying the gain of an RF amplifier.
In state-of-the-art communication systems such as Third Generation Partnership Project (3GPP) Time Division Duplex (TDD) and Frequency Division Duplex (FDD) systems multiple channels of variable rate data are combined for transmission. FIGS. 3 and 4 represent prior art open and closed power control transmission systems, respectively. Background specification data for such systems are found at 3GPP TS 25.223 v3.3.0, 3GPP TS 25.222 v3.2.0, 3GPP TS 25.224 v3.6 and Volume 3 specifications of Air-Interface for 3G Multiple System Version 1.0, Revision 1.0 by the Association of Radio Industries Businesses (ARIB).
Such open and closed loop power control systems for variable multirate wireless communications systems respond relatively slowly to data rate changes, resulting in sub-optimal performance such as relating to excessive transmitter power and below-quality received signals. It would be desirable to provide a fast method and system of power control adaption for data rate changes resulting in more optimal performance.
The invention provides a method of controlling transmitter power in a wireless communication system in which user data is processed as a multirate signal having a rate N(t) and in which the user data signal having rate N(t) is converted into a transmission data signal having a faster rate M(t) for transmission. The transmitter power is controlled by a closed loop system where the transmission power is adjusted by applying a scale factor in response to step up/down data generated by a receiver of the transmitted data, the step up/down data being based in part on relatively slowly collected quality of data. The step up/down data is determined as a function of N(t)/M(t) such that a change in the user data signal rate or the data rate of the transmission data signal is compensated for in advance of a quality of data based adjustment associated with such a data rate change. Preferably, the user data signal having rate N(t) is converted into the transmission data signal having a faster rate M(t) by repeating selected data bits whereby the energy per bit to noise spectrum density ratio is increased in the transmission data signal.
In a preferred embodiment, the step up/down data is generated by the receiver by combining measured interference power data of the signal received from the transmitter with target signal to interference ratio (SIR) data which is computed by multiplying nominal target SIR data, based on relatively slowly collected received signal quality data, by a factor N(t)/M(t) so that the target SIR data is quickly adjusted when a change in data rate occurs. Additionally, the transmitter computes the scale factor based on the received step up/down data and √{square root over ( )}(N(t)/M(t)).
The invention also provides a closed loop transmission power control system for a wireless communication system in which user data is processed as a multirate signal having a rate N(t) and in which the user data signal having rate N(t) is converted into a transmission data signal having a faster rate M(t) for transmission and in which the transmission power is adjusted by applying a scale factor in response to step up/down data. The system includes a receiver which receives the M(t) rate transmission data signal and generates the step up/down data. The receiver preferably has a data signal rate converter which decreases the data rate of received transmission data M(t) to produce a user data signal having a lower rate N(t), a data quality measuring device for measuring the quality of data of the user data signal, and circuitry for computing step up/down data based in part on the measured quality of data of the user data signal. The data signal rate converter is associated with the circuitry to provide rate data such that said circuitry computes step up/down data as a function of N(t)/M(t) such that a change in the user data signal rate or the rate of the transmission data signal is compensated for in advance of a quality of data based adjustment associated with such data rate change.
The system also preferably includes a transmitter having a data signal rate convertor which converts the user data signal having rate N(t) into the transmission data signal having a faster rate M(t) by repeating selected data bits whereby the energy per bit to noise spectrum density ratio is increased in the transmission data signal.
In a preferred embodiment, the receiver has an interference measuring device for measuring the power of an interference signal received with the M(t) rate transmission data signal. The data quality measuring device outputs a nominal target SIR data based on relatively slowly collected received data quality data. The receiver circuitry computes the step up/down data by combining measured interference power data of the signal received from the transmitter with target signal to interference ratio SIR data which is computed by multiplying the nominal target SIR data by a factor N(t)/M(t) so that the target SIR data is quickly adjusted when a change in data rate occurs.
Additionally, in the preferred embodiment, the transmitter includes a processor which computes the scale factor based on the step up/down data and √{square root over ( )}(N(t)/M(t)).
Other objects and advantages will be apparent to those of ordinary skill in the art based upon the following description of presently preferred embodiments of the invention.